1. Field of the Invention
The present invention relates to a controlled-release composition comprising a drug-containing core coated with a coating composition comprising a water-insoluble substance and a swellable polymer having no basic groups.
2. Description of the Related Art
Controlled-release preparations of drugs, especially sustained-release preparations, are advantageous in that administration frequency can be reduced by maintaining a constant plasma concentration of drug over an extended period of time to ensure sustained effect of the active ingredient. In addition, such preparations are also expected to decrease side effects by suppressing the rapid rise in the blood level of drug. Therefore, a large number of controlled-release systems, including capsular preparations comprising a drug-containing core coated with a release-controlling film (Japanese Patent Unexamined Publication Nos. 145056/1995 and 206679/1995, Canadian Patent Unexamined Publication No. 2,068,366, WO 94/22431, EP0377518, EP0630646, EP0631781, Japanese Patent Examined Publication No. 72130/1995). In such capsular preparation, the release-controlling film is made of the hydrophobic polymer containing a hydrophilic or a water-soluble substance, and release or releasing rate of the drug is designed to control by the formula of the film.
There are many drugs whose absorption rate in the large intestine is not as good as in the small intestine. In view of the fact that controlled-release compositions in the form of oral preparations pass through the small intestine in relatively short time, for example, active ingredient generally reaches the large intestine in about 5-6 hours in such composition, it is difficult to design a sustained-release preparation of such drugs for once- or twice-a-day administration that is required to maintain an effective plasma concentration of drug for 12-24 hours, because the absorption of the drugs would be suppressed after 5-6 hours following administration. Also, even a drug absorbable from the entire gastrointestinal tract often undergoes extremely suppressed drug release in the large intestine due to drug concentration reduction in the release-controlling preparation and water loss in the lower gastrointestinal tract during passage through the gastrointestinal tract. Thus it is difficult to obtain a satisfactory sustained-release preparation, especially those of the drugs mainly absorbed at small intestine.